Recently, it becomes possible to improve air-tightness also in a space that was difficult to improve the air-tightness, such as in vehicles, according to progression of technology. In a case where many passengers are aboard such a highly air-tight vehicle for a long time, a decrease in oxygen concentration or an increase in carbon dioxide concentration will occur, resulting in headache or displeasure to passengers. Therefore, it is necessary to introduce outside air appropriately.
However, urban roads, highways and the like are polluted with contaminants, such as particulates. Therefore, considering passengers health, it is a large problem to directly introduce the outside air into a passenger compartment. As a method for solving this problem, there is a method of installing a filter at a suction port through which the outside air is introduced so as to remove the contaminants in the atmosphere, such as suspended matters.
An air conditioning system using a gas permeable membrane provided by an asymmetric membrane made of a polymeric material has been proposed (see patent document 1). This air conditioning system is configured to use an asymmetric membrane having a high gas permeation property at the suction port of air as a filter to sufficiently introduce the outside air while blocking SPM (suspended particulate matter having a particle diameter of 10 μm or less in the atmosphere). Further, the patent document 1 describes to improve a mechanical strength of the membrane using a mesh body so as to restrict breakage of the gas permeable membrane due to an external stress, and to improve the strength of the gas permeable membrane by treating a surface of the mesh body with an adhesion improver.
However, even if the strength of the gas permeable membrane is improved by these means, among gas permeable membranes described in examples of the patent document 1, there is a gas permeable membrane that is broken by pressure of approximately 40 kPa. Therefore, durability for resisting to higher pressure is required.